The present invention relates to ring laser gyroscopes, also known as ring laser gyros or RLGs, and has particular relation to RLGs which are subjected to intense translational acceleration.
When an RLG is subjected to moderate translational acceleration, it distorts moderately, thereby somewhat changing its optical path in length, shape, or otherwise. A control mirror, ordinarily used to compensate for thermally induced changes in the optical path, may additionally compensate for accelerative changes. When the RLG is subjected to intense acceleration, however, it will distort beyond the ability of the control mirror to compensate.
It might be thought that accelerative distortion of the RLG takes place in the monolithic block which holds the mirrors precisely in place. This is, in fact, the mechanism for thermal distortion. As it happens, however, the bulk of accelerative distortion takes place in the control mirror itself.
The reason for this distortion of the control mirror comes from its purpose. The purpose of a control mirror is to readily change position and/or direction. It does so in response to the force provided by a control device bonded to its rear side, typically a piezo-electric transducer (PZT). Its response to this desirable force is indistinguishable from its response to the parasitic force produced by the mass of the control mirror (and of the PZT) in response to the acceleration.
This parasitic accelerative force generally does not significantly affect the direction of the control mirror, and such minor directional changes as it does produce may generally be accommodated by suitable active alignment apparatus. However, this parasitic accelerative force, if large enough, may drive the control mirror to a position so far from its rest position as to exceed the ability of the path length control (PLC) apparatus to compensate for it. This can take place whether the control mirror is controlling path length (that is, is part of the PLC apparatus), or is controlling some other parameter or parameters.